Simon Cowell jumped out of his seat to press the golden buzzer on Saturday night.
However, some slammed Vinnie McKee's rendition of I'm Gonna Be by The Proclaimers in a signature ballad style.
Fans thought that Vinnie was an excellent singer, but questioned the style of the rendition of the song.
"No, no, no. Good voice but ruining that song," penned one person during his performance.
Although some fans were not happy that Bruno Tonioli was temporarily replaced, others seemed to be completely overjoyed.
Many viewers have claimed that KSI should replace the former Strictly star on a full-time basis.
Taking to X, one viewer claimed: "#KSI has brought so much joy and enthusiasm to #bgt despite being there for a few acts. We NEED to see more of him."
A second wrote: "I dont really know KSI but my god... PLEASE keep him over Bruno! He was so refreshing in the first half."
And a third added: "#ksi is an amazing addition to the panel and we need more of him in the future on #bgt."
Last weekend the ITV competition returned to television screens up and down the country - but despite the family-friendly show thrilling viewers on Saturday night, it also infuriated some.
It has now been revealed that more than 700 viewers logged complaints to the regulator about the show overall.
The vast majority of complaints were about Auzzy Blood’s routine - with the number published as 680.
Meanwhile, around 90 of the complainants were about nudity in Akira Ohashi’s routine.
Akira left viewers open-jawed as he showcased his naked act on Saturday night - although not everyone was impressed.
